The present invention pertains in general to methods and apparatus for removing deposits from combustion chambers of an internal-combustion engine and, in particular, to methods and apparatus for reducing and maintaining combustion chamber deposits at a low level in an internal-combustion engine while the engine is in normal use.
During operation of a spark-ignition, internal-combustion engine, deposits accumulate within the combustion chambers of the engine. In the presence of these deposits, it may be necessary to supply the engine with a fuel having a higher octane number than is required in the absence of these deposits in order to avoid objectionable knock. This octane requirement increase is often abbreviated "ORI". Due to the relatively high production cost associated with fuels havng high octane numbers, it is desirable to reduce ORI as much as possible.
An example of the use of chemically-induced knock to remove deposits may be found in U.S. Pat. No. 3,038,454. In this technique, a pro-knock or detonant material in the form of a vapor is applied to the air stream ahead of a carburetor while the engine is running at idle speed or partially open throttle. Although deposits are removed, knock intensity must be monitored with extreme care in order to avoid engine damage. For optimum results, this procedure is performed by a trained mechanic. In addition, the heavy knock produced and the requirement for a knock-inducing chemical determine that an automobile undergoing chemically-induced knock ignition treatment cannot be used for normal driving while the procedure is being performed.
In order to maintain optimal power output and fuel economy, ignition systems generally provide for a speed-dependent advance and a manifold pressure-dependent advance in spark timing. Along with a basic spark-timing advance, the speed and manifold pressure advances may be identified by the term "normal spark-timing advance".
U.S. Pat. No. 2,843,645 and No. 2,833,842, assigned to the assignee of the present invention, illustrate methods and apparatus for advancing spark timing beyond the normal spark-timing advance for the purpose of removing combustion chamber deposits by a process known as "purge ignition". During purge ignition, the spark timing is advanced for all cylinders simultaneously. This procedure is applied while the vehicle remains standing still. A trained mechanic must be employed to advance the spark timing and to retime the engine at the end of the procedure. The spark timing is uninteruptedly advanced in all cylinders for the duration of the procedure. Large clouds of black exhaust are produced.
Therefore, a need exists for a method for reducing ORI which does not require removing an automobile from normal use or the employment of a trained mechanic. Furthermore, it is highly desirable to have a technique not only for reducing any build-up of combustion chamber deposits, but also for maintaining such deposits at a relatively low level. With the increasing availability of low-cost, integrated automotive electronics, it is also desirable to have an apparatus which is integrable on a chip with these electronics in order to save on weight, space, cost, and complexity.